1. Field of the Invention
The present invention relates to a color liquid crystal display (LCD) device, and more particularly to a color LCD device having different electrode structures for red, green, and blue colors to achieve an improvement in color characteristics for an intermediate color, that is, gray.
2. Description of the Related Art
As well known, liquid crystal is a material exhibiting intermediate characteristics mesophase between solid and liquid. Such liquid crystal has a property for transmitting or shielding light in accordance with an alignment thereof. Accordingly, a desired character or image may be displayed by controlling a liquid crystal, arranged between facing electrodes, to transmit or shield light in accordance with an appropriate adjustment for the arrangement of a particular portion in the liquid crystal conducted based on a variation in the voltage applied to those electrodes. An LCD device is a display device using such a property of liquid crystal. Such an LCD device occupies an important position in the display device field in that it consumes a considerably low power consumption as compared to other devices while being capable of having various sizes from a super-miniature size to a large size and having diverse display patterns.
LCD devices utilize various characteristics to conduct a driving operation in a particular mode for displaying a desired character or image. A mode utilizing birefringence characteristics is known. For the most basic one of modes utilizing birefringence characteristics, an electrically controlled birefringence (ECB) mode is known, in which a liquid crystal controls light using upper and lower electrodes as it is aligned in a horizontal or vertical direction in accordance with a voltage applied thereto.
FIG. 1 is a view illustrating an ECB mode. In FIG. 1, the reference numeral 101 denotes transparent electrodes made of an indium tin oxide (ITO) and adapted to form an electric field in accordance with a voltage applied thereto. Also, the reference numeral 102 denotes glass substrates each adapted to provide a base for the transparent electrodes 101, the reference numeral 103 denotes polarizers for selectively transmitting or shielding light, and the reference numeral 104 denotes a liquid crystal exhibiting electro-optical operation characteristics in accordance with the electric field formed between the transparent electrodes.
For the ECB mode, there are two modes, that is, a vertical alignment (VA) ECB mode in which the state of liquid crystal is changed from a xe2x80x9cfirst statexe2x80x9d to a xe2x80x9cthird statexe2x80x9d in accordance with an application of voltage, and a homogeneous ECB mode, in which the state of liquid crystal is changed from the xe2x80x9cthird statexe2x80x9d to the xe2x80x9cfirst statexe2x80x9d.
Also, there is an LC mode in which the state of liquid crystal is changed between a xe2x80x9cfirst statexe2x80x9d and a xe2x80x9csecond statexe2x80x9d in accordance with an application of voltage using a transverse electric field system, as shown in FIG. 2. In FIG. 2, the reference numeral 201a denotes plus (+) (or minus (xe2x88x92)) electrodes, 201b minus (or plus) electrodes, 202 glass substrates, 203 polarizers, and 204 a liquid crystal, respectively.
The basic principle of the LC mode is to adjust light in accordance with an anisotropy in the refractive index of the liquid crystal and an angular relation between the mean direction of the liquid crystal and the direction of each polarizer. The transmittance T in a forward direction in such an LC mode can be expressed as follows:
T=sin2(2xcex8)sin2(xcex4/2)
xcex4=2nd xcex94neff/xcex
where, xe2x80x9cxcex8xe2x80x9d represents the angle between the transmission axis of the polarizer at the side of incident light and the direction of the liquid crystal, xe2x80x9cdxe2x80x9d represents a cell gap, xe2x80x9cxcex94neffxe2x80x9d represents an effective refractive index, and xe2x80x9cxcexxe2x80x9d represents the wavelength of the incident light.
As apparent from the above expressions, it can be found that there may be two modes for adjusting light, that is, a mode for adjusting xe2x80x9cxcex8xe2x80x9d (in-plane switching (IPS) mode) and a mode for adjusting xe2x80x9cxcex4xe2x80x9d (phase difference) (ECB mode). In the ECB mode for adjusting xe2x80x9cxcex4xe2x80x9d (phase difference) (normally, xe2x80x9cxcex8xe2x80x9d is 45xc2x0), the phase difference xcex4 is varied as xe2x80x9cxcex94neffxe2x80x9d varies in accordance with an application of voltage to the liquid crystal. In this case, the variation in the phase difference xcex4 is differently exhibited at different wavelengths, respectively. In particular, a considerable color characteristic difference is exhibited at a wavelength corresponding to gray. FIG. 3 illustrates respective variations in transmittance depending on the voltage applied in the VA-ECB mode at different wavelengths.
In order to compensate for the color characteristic difference exhibited at the wavelength corresponding to gray, as shown in FIG. 3, a scheme has been proposed in which different cell gaps are used for different colors to achieve an improvement in color characteristics. This scheme is illustrated in FIG. 4.
In FIG. 4, the reference numeral 401 denotes a common electrode, 402 color filters, and 403 black matrices, respectively. The black matrices 403 are formed at boundaries of pixels to prevent a color diffusion. These black matrices 403 serve to suppress an interference effect exhibited among neighboring colors, thereby keeping the purity of each color. In FIG. 4, the reference numerals 404 and 407 denote glass substrates, and the reference numerals 405 and 408 denote polarizers, respectively. Also, the reference numeral 406 denotes pixel electrodes respectively corresponding to red, green and blue colors, and the reference numeral 409 denotes a liquid crystal.
However, this method, in which different cell gaps are used for different colors respectively, has a problem associated with manufacturing processes. For example, where color filters are designed to have different thicknesses for different colors, respectively, it is necessary to change the characteristics of materials used in order to compensate for absolute transmittances thereof. Furthermore, it is difficult to secure a desired uniformity of cell gaps. It is also difficult to secure a desired alignment uniformity of the liquid crystal during a rubbing process. As a result, the above mentioned method has a problem in that it is difficult to secure a desired yield of the LCD process.
A lateral field induced (LFI) VA mode is also known as a mode applying the birefringence mode. For this mode, a common electrode area patterned electrode structures are provided on an upper plate and a lower plate, respectively, as shown in FIGS. 5A and 5B. The upper plate has a structure rubbed in a slit direction. In FIGS. 5A and 5B, the reference numeral 501 denotes an ITO electrode, 502 glass substrates, 503 polarizers, and 504 a liquid crystal.
In the LFI-VA mode, the alignment of the liquid crystal 504 is substantially vertical when no voltage is applied, thereby preventing light from passing through the liquid crystal. When a voltage is applied, a multi-domain structure is formed in accordance with a combined function of a transverse electric field and a vertical electric field formed by the electrode structure of the lower plate 502. The simplest diagram of this structure is illustrated in FIG. 5C. FIG. 5C schematically illustrates the mean direction of the liquid crystal exhibited at the front side when a voltage is applied in the LFI-VA mode.
In this structure, the direction of the liquid crystal at the boundary of each lower plate electrode and an associated slit is slightly twisted in accordance with an application of voltage. Also, domains arranged at both sides of each electrode exhibit different ECB characteristics in that they have different 90xc2x0 viewing angle directions, respectively. Referring to FIG. 6, it can be found that the variation in transmittance characteristics exhibited in accordance with a variation in voltage is differently exhibited at different wavelengths, respectively. This means that there is a problem associated with a variation in color characteristics for gray.
Therefore, an object of the invention is to provide a color LCD device having different electrode structures for different colors to achieve an improvement in color characteristics for an intermediate color, that is, gray.
In accordance with the present invention, this object is accomplished by providing a color liquid crystal display device including an upper plate section having a common electrode, color filters, a glass substrate, and a polarizer, a lower plate section having a glass substrate and pixel electrodes, and a liquid crystal interposed between the upper and lower plate sections, wherein the pixel electrodes have different widths for different colors, respectively, and adjacent ones of the pixel electrodes have different slit widths for different colors, respectively.
Since the color LCD device uses different pixel electrode widths and different slit widths in association with color filters of different colors, respectively, there is an advantage in that the color characteristics of the color LCD device is improved where the color LCD device is designed using a pixel electrode pattern for an LFI-VA mode or an IPS mode.